1. Field of the Invention
The present invention relates to a method of determining by numerical simulation the optimum conditions to be applied in a horizontal (or complex) well drilled through an underground reservoir, so as to progressively eliminate (restore), by flushing by means of the production fluids from the reservoir, deposits or cakes formed in at least a peripheral zone of the well, as a result of drilling and completion operations.
It is well-known to the man skilled in the art to distinguish between the cakes referred to as internal cakes, formed by mud invasion of the rock pores, and the cakes referred to as external cakes, consisting of a mud coat on the external wall of the well.
2. Description of the Prior Art
It is well-known in the art to distinguish between the cakes referred to as internal cakes, formed by mud invasion of the rock pores, and the cakes referred to as external cakes, consisting of a mud coat on the external wall of the well.
The damage caused to the formations surrounding horizontal (or complex) wells, often open holes equipped for production and constitutes a critical point for deep offshore oil fields where only a limited number of very productive wells are produced so as to obtain acceptable development costs.
The tests that can be carried out to characterize formation damage in the vicinity of a well are of early stage importance. They allow selection of the most suitable drilling fluid to minimize or reduce permeability deterioration in the vicinity of the wells and to optimize well cleaning techniques.
During the past five years, the assignee has developed a specific laboratory test equipment and procedures intended to characterize formation damage due to drilling during operations under overpressure conditions and to quantify the performances of the various cleaning techniques used in the industry, as shown in the following publications:    Alfenore, J. et al., “What Really Matters in our Quest of Minimizing Formation Damage in Open Hole Horizontal Wells”, 1999, SPE 54731,    Longeron, D. et al., “Experimental Approach to Characterize Drilling Mud Invasion, Formation Damage and Cleanup Efficiency in Horizontal Wells with Openhole Completions”, 2000, SPE 58737, or    Longeron, D. et al., “An Integrated Experimental Approach for Evaluating Formation Damage due to Drilling and Completion Fluids”, 1995, SPE 30089.
However, the surveys carried out in the laboratory are often insufficient by themselves to realistically model the production conditions to be applied in wells so as to best restore the permeability of the surrounding formations without causing sand encroachment. Modelling the procedures for restoring formations surrounding a well is of great economic interest for the production of oil fields.